Light emitting diode (LED) based light bulbs or light fixtures are generally known. These devices use high power LEDs or clusters of lower power LEDs in conjunction with reflectors, lenses and diffusers to produce either an illuminated spot or a diffuse light output distribution. These devices are generally closed “bulbs” which require the light from the LEDs to undergo multiple reflections or scattering events before the light exits the devices through a scattering or clear plate. Each time the light interacts with one of these surfaces, the optical efficiency of the devices is reduced due to absorption of light or light being scattered at unusable angles. In general these devices are limited in the optical effects that can be produced (spot focusing or diffuse scattering).
In addition, these devices have difficulty in dissipating the heat generated by the LED light sources. Due to the closed nature of the devices, heat can be trapped and built up within the closed volume of the devices. The difficulty in removing heat from these devices limits the brightness of the illumination that can be achieved for a given electrical input power because, as the temperature of the LED light sources increases, the efficacy of the LED light sources is reduced.
To remove as much heat as possible, large heat sinks can be required to provide increased surface area for thermal radiation and convection. In many applications, however, the maximum acceptable size of the devices is limited. For example, an LED-based incandescent light bulb replacement should have a size and shape within the size and shape specified for standard incandescent light bulbs. In these size-restricted cases, the volume taken up by the heat sinks reduces the available area to mount additional LED light sources. This produces a limit on the number of LED light sources that can be used in such a device and thus limits the brightness that can be achieved.